In order to obtain a higher strain measurement sensitivity, a higher phase measurement sensitivity must be achieved. This is where the second generation of digital shearography, phase-shift-technique-based digital shearography, comes into play. This technique is also simply called phase shift shearography. In phase shift shearography, the phase value is directly measured using different kinds of phase shift techniques, then the strain measurement result is calculated from the phase–strain relationships [Eqs. (2.36) through (2.43)]. Phase shift shearography can be divided into temporal phase shift shearography and spatial phase shift shearography. Temporal phase shift shearography will be discussed in detail in this chapter, while spatial phase shift shearography will be discussed in Chapters 6 through 9.
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